1. Technical Field
The present invention relates to a method for manufacturing gas generating material, and in particular relates to a method for manufacturing a gas generating material which contains a metal azide and a metal oxide and which is used for generating gas to inflate a vehicle occupant restraint, such as an airbag.
2. Description of the Prior Art
U.S. Patent Application Ser. No. 528,144 filed May 24, 1990, now U.S. Pat. No. 4,994,212, assigned to the assignee of the present application, and entitled "Process for Manufacturing a Gas Generating Material" discloses a process for manufacturing an azide-containing gas generating material. The gas generating material is formed by preparing a wet mixture of a metal azide and a metal oxide. During tile manufacturing process, the formation of hazardous hydrazoic acid fumes (HN.sub.3) is minimized by: (1) maintaining the wet mixture of the metal azide and metal oxide at a temperature not exceeding 30.degree. C. and (2) maintaining the pH of the wet mixture of the metal azide and metal oxide at a value which is at least about 10.5. During the processing of the wet mixture of gas generating material, the mixture is repeatedly ground to reduce the particle size of one or more of the ingredients of the mixture. Once the wet mixture of gas generating material has been formed, excess liquid is removed from the mixture and the mixture is processed to form spheres granules which are molded to form bodies of gas generating material.
Canadian Patent 1,087,852 also discloses a process for making gas generating material.. In the process sodium azide is dissolved in heated water, and a metal oxide is added to the sodium azide water solution. The solution with the metal oxide added is then mixed to coat the metal oxide with sodium azide, and the coated metal oxide particles are recovered. Preferably, the coated metal oxide particles are recovered by evaporation of the water. The patent also refers to recovering the coated metal oxide particles by precipitation but does not explain how this is done.